What is Magnetic Flux Leakage?

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  • Written By: T. L. Childree
  • Edited By: Jenn Walker
  • Last Modified Date: 12 November 2019
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Magnetic flux leakage typically refers to a method of testing structures made of steel for metal loss caused by corrosion. In this type of testing method, the structure is magnetized, and a detector is used to detect areas in which the magnetic field is "leaking." This leakage can indicate areas where pitting or corrosion exists. A chart recording is made of the leakage field for the purpose of identifying any damaged areas of the steel structure.

Steel pipeline testing using a magnetic flux leakage tool is usually performed by placing the device inside of the pipe. The tool is then allowed to travel inside the pipeline along with whatever liquid or gas product the pipe may be transporting at the time. As the device travels along pipeline, advanced electronics on board collect real-time data to accurately detect any damage found. As the results are recorded, technicians are able to pinpoint the exact type of damage found and its location in the event that some type of repair work is needed.


A typical magnetic flux leakage testing device consists of two bodies that are commonly referred to as the magnetizer and the electronics can. The magnetizer body contains powerful magnets and brushes along with sensors that are used to detect leakage. As the device travels along the steel structure, the magnets and brushes form a type of magnetic circuit with the steel, while the sensors monitor this circuit for any possible interruptions. Some type of corrosion or damage to the steel structure usually causes interruptions to the circuit.

The electronics can of the testing device typically contains several different pieces of equipment that are used to help pinpoint the exact location of the magnetizer body. At the rear of this device are a speedometer and odometer used to measure both the speed of the magnetizer and the distance that it travels. Many times, a Global Positioning System (GPS) tracking device is also used to further locate the device.

Magnetic flux leakage testing is sometimes performed using a high-resolution device that contains a larger number of sensors than the standard version. High resolution testing typically provides information that is more detailed and reliable. The superior information obtained from this form of testing often prevents unnecessary digging of steel pipelines and draining of steel tanks for further inspection.


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